Thread draw-off nozzles have become known in the state of the art in many designs for open-end rotor spinning devices. Such thread draw-off nozzles have the task of deflecting the spun yarn upon being drawn off from the spinning device and giving the drawn-off yarn a false twist. Since, in the freshly spun yarn, the true yarn twist is introduced predominantly between the thread draw-off nozzle and the draw-off device, but does not propagate sufficiently into the rotor groove, the spin stability can be substantially increased by introducing a false twist by means of the thread draw-off nozzle. To introduce the false twist, the thread draw-off nozzles feature surface structures, which, in principle, have proven to improve spinning stability, but at the same time also have a considerable influence on the quality of the spun yarn. Spiral elevations or radially arranged notches are predominantly used as surface structures. In general, spiral nozzles are considered to be advantageous for yarn quality, but frequently offer less spin stability. On the other hand, notched nozzles are well-suited to increase spinning stability, but are considered more aggressive with respect to yarn quality.
As such, efforts have already been made to find a thread draw-off nozzle that meets both requirements in equal measure. For example, DE 199 06 111 A1 proposes a thread draw-off nozzle with notches arranged radially in the area of the nozzle funnel, whereas the notches are configured asymmetrically. The asymmetric notch is formed such that the thread first passes over a very flat inlet wall gently into the notch base, where it is then abruptly stopped by the steep baffle wall. Given this asymmetric configuration of the notches, the skipping over of the notches by the circumferential thread is avoided.
According to DE 103 18 305 A1, it is provided that a thread draw-off nozzle is provided with radially extending, asymmetrical notches, which are curved in a sickle-shaped manner. The curvature of the notches is designed to be counter to the curvature of the crank-like circumferential yarn. This is to be able to achieve a different effect on the yarn by means of a single notch. Thus, in the area of the front surface, an increased false twist effect is to be achieved, which improves spinning stability, while, in the direction of the yarn draw-off channel outweigh, it is to outweigh the effect of the baffle wall, which temporarily stops the thread.